Previous work by this group has explored some of the biochemical events that affect cell cycle G2 delay and determined how radiation affects these events. Irradiation of HeLa cells and other cells reduces levels of cyclin B1 mRNA. To determine how this occurs as well as to gain an understanding of how cyclin B1 mRNA levels are regulated in control cells, this proposal is aimed at evaluating contributions of transcription and of post transcriptional controls to cyclin B1 mRNA levels. This work will add to our knowledge of the controls regulating the transition of cells through the cell cycle and will indicate how those controls are perturbed after irradiation or treatment with DNA damaging agents.